The present invention relates to an improved rotation angle detector, and more particularly relates to improvement in the construction of an optical interceptor used in a rotation angle detector made up of a combination of a photoelectric transducer and the optical interceptor and used for a rotatable or turnable object.
In order to carry out successful detection of extremely small angular deviations of a rotatable or turnable object from the standard angular position with high accuracy, it is required that the torque restraining the rotation or turning be negligible, or at least extremely small, and the thermal coefficient of the detection circuit should be extremely small.
Magnetic systems, electrostatic capacity systems and induction systems have been conventionally utilized for rotation angle direction. However, no such conventional system can assure a sufficient degree of accuracy in practice, because of the restraining torque problem.
Photoelectric systems are known to be advantageously suited for rotation angle detection due to their freedom from the restraining torque problem. Such systems are in general made up of a photoelectric transducer and an optical interceptor, the photoelectric transducer including a light source and a light receptive element facing each other and the optical interceptor including a light interceptor interposed between the light source and the light receptive element. The optical transmittancy of the light interceptor varies from position to position on the surface thereof. Angular deviation, i.e. rotation or turning, of the object from its standard angular position induces corresponding relative rotation between the photoelectric transducer and the optical interceptor, and the magnitude of the angular deviation of the object from the standard angular position is represented by the change in the transmissive optical quantity caused by the above-described relative rotation.
In the construction of the conventional photoelectric rotation angle detector, the above-described light interceptor is perpendicular to a supporting shaft it is mounted on, and the optical trace between the light source and the light receptive element runs through the light interceptor. That is, assuming that the above-described supporting shaft extends in the vertical direction, the light interceptor extends in the horizontal direction, and the light source is located spacially on one side, e.g. the upper side, of the light interceptor whereas the light receptive element is located spacially on the other side, e.g. the lower side, of the light interceptor.
In order to assemble a conventional detector of a movable optical interceptor type, it is necessary to first fix the light source and the light receptive element within a casing, secondly interpose the light interceptor between the light source and the light receptive element, thirdly insert the supporting shaft through the light interceptor and finally mount the supporting shaft and the light interceptor in a rotatable fashion within the casing. Thus, assembling the conventional rotation angle detector in general requires highly complicated, highly technical and disadvantageously time-consuming manual operations, which and replacement of the light interceptor and maintenance of the mechanical parts is very inconvenient and difficult.